Conductivity behavior and solid state NMR investigation of imidazolium-based polymeric ionic liquids

Novel proton-conducting anhydrous polymer electrolytes comprising imidazolium ionic liquid units in the polymeric structure have been synthesized. These polymeric ionic liquid electrolytes were doped with phosphoric acid to get Poly(AcIm-n)xH(3)PO(4), where x is the number of moles of H3PO4 per polymer repeat unit and n is the number of alkyl spacers (-CH2). Thermogravimetric analysis (TGA) illustrates that these materials are thermally stable up to about 200 degrees C. DSC results show the softening effect of the length of the spacers as well as phosphoric acid. Mechanical studies displayed the cross-linking of the samples which were also confirmed by solid state P-31 CPMAS NMR spectra. The proton conductivity of the samples increases with x and reaches 10(-2) S cm(-1) at 120 degrees C for both Poly(AcIm-2)2H(3)PO(4) and Poly(AcIm-6)2H(3)PO(4). The conductivity isotherms show that the proton transport in acid-doped polymeric ionic liquids obeys VTF behavior. (C) 2010 Elsevier B.V. All rights reserved.